Manufacture of sodium bichromate.



' of Manchester,

concentrated by the boiling.

UNITED s'ra'rs rrnnr ornroia.

THOMAS JOHN IRELAND CRAIG, OF MANCHESTER, ENGLAND, ASSIGNOR TO PETER SPENCE & SONS LIMITED, 0F MANCHESTER, ENGLAND.

MANUFACTURE OF SODIUM BICHROMATE.

99%,1219. No Drawing.

Specification of Letters Patent. Application filed October 8, 1910. Serial No. 585,991.

Patented June a, rear.

To all whom it may concern: I

Be it knpwn that I, THOMAS JOHN Inn- LAND CRAIG, D. So, a subject of the King of Great Britain and Ireland, and a resident England, have invented a new and useful Manufacture of Sodium. Bichromate, of which the following is a specification.

In the manufacture of sodium bichromate as described in the specification to U. S. A. Patent No. 725,501, dated the 1 1th day of April, 1903, apart of the process consists in driving oii by boiling in a suitable closed vessel, the ammonia from a solution containing ammonium chromate and sodium chromate, such solution being at the same time It has since been ascertained in practice that the elimination of ammonia from the solution is assisted before its concentration or boiling in the closed vessel described, a current of steam.

' This method of treating the liquor however,

consumption of fuel to raise the necessary steam. q Incarrying my present invention into effect .for the removal of ammonia fgom a solution containing, ammonium chromate and sodium chromate, I concentrate the solution to a highdegree. by boiling, for example to a sp. g. of about ing point, 6. approximately 120 degrees centigrade, and then pass into it in a suitable vessel, for example a still, steam at a tem erature well. abo've'the boiling point of the iquor at about this degree of concentration. Such steam I will, for the purposes of this invention, v call high temperature steam, and it may be obtained by generation under the necessary pressure to give the required temperature or by superheating. The remaining ammonia contained in the concentrated solution is readily removed as far as is desirable by this treatment.

The passage of the high temperature steaminto the concentrated solution may be i the only .passage of steam into the liquor in carrying out is preferred trated solution concentrating and boiling .vessel by passing,

into it steam which is given off by and from in the county of Lancaster,-

required is less than one-tenth by passing into the liquor- 1.85 at its boil solution which is being boiled and concentrated. With this preliminary treatment of the solution with steam which is 'iven 0E by the solutlon being boiled and concentrated and with the treatment of the concentrated liquor with high temperature steam, a very large economy in the amount of fuel neces-- sary for steam raising is effected. Practical tests have shown, for example, that by this Improved process the amount of such fuel I of that required by the prior process in use.

The temperature of the steamemployed may vary within wide limits provided it is applied at a temperature well above the boiling point of the concentrated liquor Imay for example emunder treatment. ploy dry steam at a. pressure of about 100 lbs. per square inch or I may, as a further example, superheat steam at a'pressure of about seventy-five pounds per square inchto a temperature of about 300 G.

I may employ pressure to raise the boiling point of the concentrated liquor and thus assist the action of the higher temperature steam which is passing into it. j

What I claim is 1. In the production of sodiumbichromate, removing ammonia from a concentrated solution containing sodium chromate and ammonium ohromate by passing hig temperature steam into such concentrated solution, substantially as set forth.

2. In the production of sodium bichromate, removing ammonia from a concentrated solution containing sodium chromate and ammonium chromate and which solution is under pressure, perature steam into such concentrated solu tion While under pressure, substantially as set forth.

3. In the production of sodium blCllI'O- mate by the removal of ammonia from a solution containing sodium chromate and ammonium chromate, treating the uncon' centratecl solution with steam derived from solution which is being boiled and concentrated and treating the concentrated solution with high temperature steam substantially as set forth. I

4. In the production of sodium ,b1chromate by the removal of ammonia from a solution containing so ium chromate and ammonium chromate, treating the unconmy hand in the presence of two subscribing i centrated solution with steam derived from Witnesses.

solution which is being boiled and concentrated and treating the concentrated solu- 5 tion under pressure with high temperature \Vitnesses:

steam, substantially as set forth. WILLIAM G120. HnYs, In witness whereof I have hereunto set JOHN OCONNELL.

THOMAS JOHN IRELAND CRAIG. 

